Disc drives are data storage devices that store digital data in magnetic form on a rotating storage medium on a disc. Modern disc drives comprise one or more rigid discs that are coated with a magnetizable medium and mounted on the hub of a spindle motor for rotation at a constant high speed. Information is stored on the discs in a plurality of concentric circular tracks typically by an array of transducers ("heads") mounted to a radial actuator for movement of the heads relative to the discs. Each of the concentric tracks is generally divided into a plurality of separately addressable data sectors. The read/write transducer, e.g. a magnetoresistive read/write head, is used to transfer data between a desired track and an external environment. During a write operation, data is written onto the disc track and during a read operation the head senses the data previously written on the disc track and transfers the information to the external environment.
Radial actuators employ a voice coil motor (VCM) to position the heads with respect to the disc surfaces. The actuator VCM includes a coil mounted on the end of the actuator body opposite the head arms so as to be immersed in the magnetic field of a magnetic circuit comprising one or more permanent magnets and magnetically permeable pole pieces. When controlled direct current (DC) is passed through the coil, an electromagnetic field is set up which interacts with the magnetic field of the magnetic circuit to cause the coil to move in accordance with the well-known Lorentz relationship. As the coil moves, the actuator body pivots about the pivot shaft and the heads move across the disc surfaces. The actuator thus allows the heads to move back and forth in an arcuate fashion between an inner radius and an outer radius of the discs.
Minimizing structural vibration within the disc drive is critical to maintaining proper head positioning within a track, as well as to maintaining proper disc drive integrity. It is, therefore, highly desirable to experimentally evaluate the effects structural vibrations have within a disc drive and, further, to test possible solutions for preventing and minimizing anticipated structural vibrations which could arise under normal or predetermined disc drive operating conditions and handling conditions.
Structural vibration testing of disc drives is well known. Conventionally, structural vibration testing occurs though the use of a shaker apparatus, in which the subject disc drive is secured to the shaker apparatus and shaken in a reciprocal linear motion fashion, i.e., shaken back and forth, side to side, or up and down. Linear external energy is inputted into the disc drive to simulate structural vibrations introduced into a disc drive during normal operating conditions by fastening the drive to a shaker table and vibrating or oscillating the table in accordance with a predetermined acceleration profile. A key shortcoming to the use of a conventional "linear" shaker apparatus is that the operating disc drive is sensitive to both linear and rotational energy. In fact, since the late 1980s/early 1990s when a rotational actuator, instead of a linear actuator, was introduced into disc drive unit, the rotational component of structural vibrations is the predominate energy component responsible for disrupting proper head positioning within a disc drive track. Additionally, it is known in the art that rotational vibrations have other disruptive effects on disc drive operation and integrity. However, there has been no direct means of testing drives for these rotary vibrations. Accordingly, there is a need in the disc drive art for a disc drive shaker apparatus which can produce a predominately rotational energy spectrum for subjecting disc drives to rotational accelerations. Such a device can be used in accurately and more realistically testing and characterizing disc drives function under normal and predetermined operating conditions.